The present disclosure generally relates to gas turbine engines, and, more specifically, to film cooled slotted walls therein such as those found in rotor blades, stator vanes, combustion liners and exhaust nozzles.
Gas turbine engines include a compressor for compressing ambient airflow, which is then mixed with fuel in a combustor and ignited for generating hot combustion gases. These hot combustion gases flow downstream over rotor blades, stator vanes, and out an exhaust nozzle, for example. In order to provide a suitable working-life of these components, they need to be suitably cooled. For example, a rotor blade or stator vane includes a hollow airfoil, wherein the outside of the airfoil is in contact with the combustion gases and the inside of the airfoil is provided with cooling air for cooling the airfoil. Film cooling holes are typically provided through the wall of the airfoil for channeling the cooling air through the wall for discharge to the outside of the airfoil to form a film cooling layer of air to protect the airfoil from the hot combustion gases.
In order to prevent the combustion gases from flowing backwardly into the airfoil through the film holes, the pressure of the cooling air inside the airfoil is maintained at a greater level than the pressure of the combustion gases outside the airfoil. The ratio of the pressure inside the airfoil to the pressure outside the airfoil is commonly referred to as the backflow margin. Further, the ratio of the cooling air mass velocity (the product of air velocity times density) to the mass velocity of the hot combustion gases along the outside of the airfoil is sometimes referred to as the blowing ratio.
Film cooling performance may be characterized in several ways. For example, one relevant indication of performance is referred to as the adiabatic wall film cooling effectiveness, which is referred to hereinafter as the cooling effectiveness. This particular parameter is related to the concentration of film cooling fluid at the surface being cooled. In general, the greater the cooling effectiveness, the more efficiently the surface can be cooled. A decrease in cooling effectiveness causes greater amounts of cooling air to be employed to maintain a certain cooling capacity, which in turn diverts air away from the combustion zone. This diversion of air can lead to problems, such as greater air pollution resulting from non-ideal combustion, and less efficient engine operation.
Accordingly, a continual need exists for improved film cooled walls to increase cooling effectiveness.